In a typical cellular radio communications system (wireless communication system), an area is divided geographically into a number of cell sites and sectors, each defined by a radio frequency (RF) radiation pattern from a respective base transceiver station (BTS) antenna. The base station antennae in the cells are in turn coupled to a base station controller (BSC), which is then coupled to a telecommunications switch or gateway, such as a mobile switching center (MSC) or packet data serving node (PDSN) for instance. The switch or gateway may then be coupled with a transport network, such as the Public Switched Telephone Network (PSTN) or a packet-switched network (e.g., the Internet).
When a mobile station (i.e., any wirelessly equipped client device (whether movable or in fixed position), such as a cellular telephone, pager, or appropriately equipped portable computer or personal digital assistant, for instance) is positioned in a cell, the mobile station communicates via an RF air interface with the BTS antenna of the cell. Consequently, a communication path can be established between the mobile station and the transport network, via the air interface, the BTS, the BSC and the switch or gateway.
Data communications over the air interface between a mobile station and a base station generally proceed according to a designated air interface protocol, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), or any other air interface protocol now known or later developed. Air interface communications from the base station to the mobile station constitute “forward link” or “downlink” communications, while those from the mobile station to the base station constitute “reverse link” or “uplink” communications.
The speed or rate at which data is transmitted between a base station and a mobile station can vary from protocol to protocol and can further vary based on a number of factors, such as propagation loss, building and landscape obstructions, and multi-path fading for instance.
Certain air interface protocols provide for largely symmetric communication between a base station and a mobile station, in that the data rate provided on the forward link is substantially similar to the data rate provided on the reverse link. CDMA 1xRTT (1xRTT) is an example of such a symmetric protocol.
As defined by well known industry standards such as IS-2000 for instance, 1xRTT allows multiple mobile stations in a cell sector to communicate on the same frequency and at the same time as each other. Communications between the base station and a given mobile station are distinguished from those between the base station and other mobile stations by modulating the communications with one or more codes unique to the mobile station. Each forward link traffic channel, for instance, is defined in part by modulating with a “Walsh Code” assigned for use by the mobile station. And each reverse link traffic channel is defined in part by modulating with a “long code” associated with the mobile station. Fundamental traffic channels under 1xRTT generally support up to 9.6 kbps or 14.4 kbps respectively on both the forward link and reverse link, although supplemental traffic channels can also be used (on both the forward link and reverse link) to moderately increase the data rate.
Other air interface protocols, in contrast, provide for largely asymmetric communication of data, by providing a substantially higher data rate on the forward link than on the reverse link. Such air interface protocols leverage the fact that, with most IP traffic, the forward link carries a heavier load than the reverse link (as users tend to download far more than they upload). CDMA 1xEV-DO (EV-DO) is an example of such an asymmetric protocol.
In a EV-DO system, as defined by well known industry standard IS-856 for instance, the forward link uses time division multiplexing, in order to allocate all of the transmission power in a sector to a given mobile station at any moment, while the reverse link retains largely the traditional 1xRTT code division multiplexing format, albeit with the addition of a “data rate control” (DRC) channel used to indicate the supportable data rate and best serving sector for the forward link. The end result is that an EV-DO forward link data rate can theoretically support from 38.4 kbps to 3.1 Mbps, while the EV-DO reverse link is limited to the lower data rate more typically provided by 1xRTT. In addition, EV-DO provides an “always on” connection, in which a mobile station can quickly engage in wireless data communications. This “always on” connection mode, combined with EV-DO's high speed forward link, makes EV-DO an attractive alternative to more traditional wireline data communications.
While wireless data communications are most often used to facilitate communication between end-user devices (such as cell phones) and base stations, the industry has also recognized that wireless data communications can be advantageously used to provide wireless backhaul communications between network components. By way of example, rather than incurring the expense of installing and maintaining a T1 line or other landline connection extending from a BSC to a BTS, a wireless carrier can set up a wireless data connection such as a 1xRTT or EV-DO connection from the BSC to the BTS. To do so, the wireless carrier may equip the BSC with an antenna and circuitry to function largely like a base station, and the carrier may equip the BTS with circuitry (and another antenna, if necessary) to function largely like a mobile station (albeit fixed). Backhaul data (including bearer traffic and overhead control data) can then flow wirelessly between the BSC and the BTS. Similarly, a wireless backhaul connection can be provided to extend coverage from a BTS out to a remote BTS or distributed antenna system (DAS), by setting up the remote BTS or DAS to function largely like a mobile station so as to receive data wirelessly from the serving BTS.